Plant cell requirements

Carbon dioxidefor photosynthesis

Organic nutrientse.g. sugars for

respiration

Oxygen for respiration

Inorganic ions & water

Stomata

RootsMakes it

Stomata

Mammals – have faster chemical reactions happening in cells. E.g. theyHave a faster rates of respiration and As result need more O2 & glucose.

Plants – have slower rates of respiration

They will have very different transport systems

Plant transport systems

Moves products of P

PHLOEM TISSUE

Process is calledTRANSLOCATION

Moves water fromroots upwards

XYLEM VESSELS

Process is calledTRANSPIRATION

ROOT HAIR CELLS

ROOTS

XYLEM

LEAVES

SOIL

ATMOSPHERE

AREA of HIGH Ψ

AREA of LOW Ψ

The structure of a root

If water is to pass through to the xylem in the stem, it must move

through several types of cell/structures.

Tough epidermis

Root hairs

Cortex

Stele

Endodermis

Casparian strip

The structure of a root

STELE

XYLEM

PERICYCLE

ROOT HAIR

PHLOEM

CORTEX

ENDODERMIS

EPIDERMIS

How water enters a

plant

Soil particle

Water particle

Gas

Water with inorganic ions

Root hair: with dissolved

materials of cellAREA of HIGH Ψ

AREA of LOW Ψ

RESULT: water enters the root

hair

How water enters a

plant

Osmosis

AREA of HIGH Ψ

AREA of LOW Ψ

How water enters a

plant

Osmosis

AREA of HIGH Ψ

AREA of LOW Ψ

How water enters a

plant

Osmosis

AREA of HIGH Ψ

AREA of LOW Ψ

How water enters a

plant

Osmosis

AREA of HIGH Ψ

AREA of LOW Ψ

Xylem

The previous slide is simplistic………

Before water gets to into the xylem, it must travel through the cortex and into the central structure – the stele.

STELE

XYLEM

PERICYCLE

ROOT HAIR

PHLOEM

CORTEX

ENDODERMIS

EPIDERMIS

Water moves through roots in two ways:

1.APOPLAST PATHWAY

2.SYMPLAST PATHWAY

Water moves through roots in two ways:

SYMPLAST PATHWAY

APOPLAST

PATHWAY

APOPLAST

PATHWAY

SYMPLAST

PATHWAYBoth are routes for water through the cortex to

the stele

Water moves from cell to cell by passing along

cell walls

Water moves into cell through

vacuole/cytoplasm and into next cell via plasmadesmata

This route stops at the ENDODERMIS

This route continues into the stele and supplies the xylem

The Endodermis has a ring called the

CASPRIAN STRIPThis is made of a wax

called SUBERIN

This stops water movingthu. the APway

Xylem tissue

Fibres-elongated, lignified

-dead, act as support

Parenchyma cells-Normal plant cells

-No P role-Isodiametric

Tracheids Vessel elements

Invovled in water transport

There are 4 types of xylem vessels

Xylem vessels aremade up of dead

cells with thickenedcell walls - LIGNIN

There is no movement betweenvessels – hole are filled with cellulose

Vessel element

Remains of old cell walls

Lumen

Lignified cell walls

XYLEM VESSELS TRACHEIDS

Both are tubes through which water moves up a plant

Open ends Tapered ends

Dominant method of water

movement in modern plants

Dominant method of water

movement in PRIMITIVE plants

Structure of a leaf CuticleUpper

Epidermis

LowerEpidermi

s

Palisade

cellsSpongy

Mesophyll

cells

Guard cell

(stomata)

Vasculartissue

Air spaces

Spongy mesophyll

cells

Upper Epidermis

Stomata

Guard

cell

Vascular tissue

Palisade

cells

Water moves up the xylem vessel

Water leaves the xylem vessel thru

a pit

Water moves from cell to cell via

osmosis

Water leaves SMcells, entering

the air space

Water vapour diffuses out of

stomata

Often there is a water potential

gradient btwn the cells and the atmosphere

This ensures rapid water loss from

stomata

This loss is calledTRANSPIRATION

Environmental factors that increase the rate of transpiration

Warm/hot

Windy

Dry

There is a high water potential gradient between the

environment and the spongy mesophyll

Environmental factors that decrease the rate of transpiration

Cold

Wet

Still

There is a low water potential gradient between the

environment and the spongy mesophyll

If there is a large loss of water from the SMcells into the atmosphere, this will reduce the

hydrostatic pressure from the top of the

xylem

Low hydrostatic pressure

High hydrostatic pressure

Water gets sucked updue to the h’static

differences

Section of a xylem vessel

COHESION: water molecules are attracted

to each other

ADHESION: water molecules are attracted to the lignin in the xylem

vessels

ADHESION & COHESION ensures there is a constant stream of water running through the xylem vessels AKA MASS FLOW

ROOT PRESSURE

Some plants help transpirationby increasing the water pressure

At the base of xylem vessel

This is done by pumping solutes into the xylem

in the root

This is done viaACTIVE

TRANSPORT

This increases the rate at which water Flows into the xylem via osmosis

This is not adominant force in

transpiration

Active pumping of solutes into the xylem

Water follows down the WP gradient

MEASURING THE RATE OF TRANSPIRATIONUSING A POTOMETER

Tube with a scale

Water filled tube

Air tight seal

Plant cutting

Select plant to be used in the experiment.

Underwater, make a cut an angular cut (33o),

separating the main plant from the cutting you are

using.

Keep the cutting beneath the water level,

this ensures the column of water in

the xylem is not broken.

Fill the potometer with water,

being sure to introduce an air bubble into the capillary

tube.

Then place the whole Potometer under water,

and carefully insert the top of the cutting into the top of the

potometer – it is vital all this is done underwater.

The plant can now be exposed to different environmental conditions and the rate of wateruptake can be measured.

We are assuming, that the rate of water uptake = the rate of transpiration.

Results can be graphed as follows; rate of water transpired (µm3 per second) against time.

XEROPHYTES – plants adapted to low water conditions

E.G. Marram grass Ammophila arenaria

Rolled leaf

Leaf hairs

Sunken stomata

Waxycuticle

All are structural adaptations to lowering the rate of transpiration

What other adaptations have the following species evolved to cope with water stress?

Opuntia

Sitka spruce

Phlomis italica

Euphorbia canariensis

See page 139